The present invention relates to resins obtained by Diels-Alder polymerization, and more particularly, to high temperature tolerant thermoset resins obtained by Diels-Alder polymerization of benzocyclobutene-alkyne imide monomers
The Diels-Alder reaction is a cycloaddition reaction in which an unsaturated group, which is a dienophile, combines with a 1,3-diene to form a six membered ring. The Diels-Alder reaction appears to be favored by the presence of the diene's electron-yielding groups, and the dienophile's electron-attracting groups. Although the Diels-Alder reaction is used extensively in organic chemistry, it is less commonly employed in polymer chemistry. At high temperatures, most Diels-Alder adducts undergo conversion to other products, such as aromatic rings, before the temperature required for the reverse reaction is reached; consequently, most Diels-Alder polymers exhibit high thermal stability.
In most Diels-Alder polymerizations, a bisdiene reacts with a bisdienophile. For example, in W. J. Bailey et al., "Polymeric Diels-Alder Reactions," J. Org. Chem. 27, 3295 (1962), 2-vinylbutadiene, a bifunctional diene, is reacted with benzoquinone, a dienophile. J. K. Stille, "Cycloaddition Polymerization," Die Makromolekulare Chemie 154,49 (1972), teaches that cyclopentadienones undergo a variety of Diels-Alder reactions depending on the ring substitution, dienophile, and reaction conditions. To obtain a monoadduct, cyclopentadienone is employed with an acetylenic dienophile to obtain an aromatic product. Additionally, R. T. Kohl et al., "Diels-Alder Reactions of Phenyl-Substituted 2-Pyrones: Direction of Addition with Phenylacetylene," Macromolecules 11,340 (1978) shows the Diels-Alder reactions of substituted acetylenes with 2-pyrones. J. N. Braham et al., "Polyphenylenes via Bis (2-pyrones) and Diethynylbenzenes, The Effect of m- and p-Phenylene Units in the Chain," Macromolecules 11,343 (1978) shows the Diels-Alder 4+2 cycloaddition reaction of bis (2-pyrone) monomers with diethynylbenzenes.
In some Diels-Alder polymerizations, the same molecule contains both a diene and a dienophile moiety. W. J. Bailey, "Diels-Alder Polymerization," Step-Growth Polymerization, Marcel Dekker, New York, 1972, stresses that this type of polymerization presents considerable difficulty. One class of monomer is capable of functioning as both a diene and a dienophile. Cyclopentadiene and 2-vinylbutadiene are two examples. In another class of monomer, the diene and dienophile are different. Meek and Argabright, J. Org. Chem. 22, 1708 (1957) prepared 6-[p-(p-maleimidobenzoyloxy)-phenyl]-1,2,3,4-tetrachlorofulvene which contains a maleimido group as a dienophile and a perchlorofulvene group as a diene.
Bis-benzocyclobutenes and polymers derived therefrom are disclosed in U.S. Pat. No. 4,540,763. The bis-benzocyclobutenes are connected by direct bond or a bridging member such as a cyclic imido group. In general, the polymers are obtained by addition polymerization wherein the fused cyclobutene rings undergo thermal transformation to an o-xylylene moiety which can react with one another.